I can think of a couple of experimental ways to test this but most are kind of complicated to set up. Here’s a simple way to test it- pump up your shock/fork and then slowly start to unscrew it. As soon as you hear the first little hiss or see the gauge start to drop, stop unscrewing it and wait until the gauge reaches zero as the air slowly leaks out. At this point your shock or fork should have collapsed if it was leaking air but just to be sure, reverse direction and screw the pump back on and you should see the gauge pop back up to high pressure (less whatever comes out to equalize in the pump).
Typically the pumps are designed to disengaged from the valve stem allowing it to close before losing the air seal. For what it’s worth I did test this just now with a Fox 36 I had laying around and my Filzer pump from MEC- no pressure loss from the fork other than what came out when I re-engaged the pump.
You dont lose any pressure when you dettach the pump since it is still pressurized. I believe you have bontrager with the red knob, that red knob will release the schader valve closing it while it is still pressurized. On the other hand, you will lose a little pressure when attaching it because pressure will leaked to the tube connected to the gauge.
That isn’t what I was saying. I wasn’t saying you lose pressure removing the pump I have (and yes it is the Bontrager with the red knob). I was saying I think you would lose pressure removing a pump without the additional valve.
It can’t leak from the suspension until the pressure in the pump is reduced. If the pressure in both is equal there can be no movement between the two. Simple physics.
So to clarify, you are saying you attached the pump, equalized the pressure between the shock and the pump, took a reading, then removed the pump. At which time there had to be some sound of air loss, at a minimum from the pressure in the pump/hose from releasing. Then reattached the pump at which time there would have been a pressure drop from reattaching the pump and equalizing the pressure. I fail to see how you cold determine there was no loss, its impossible to test that way.
I 100% agree with that statement. But until the time at which the two system are physically separated, any air would leak equally from both systems, it’s simple physics.
I have the bontrager as well. but for those pump that does not have the red knob. I believe it designed in such a way that when you start unscrewing the pump valve, it will close up the schrader valve while it is still pressurized. And the hissing sound of air is the one that coming from the the pump. If it isnt designed that way. Im glad i got the bontrager one:blush:
No, you’ve misunderstood. I probably didn’t word that well. The pump doesn’t get removed. The goal is to prove that the shock is sealed before the pump loses it’s seal. The pump is slowly loosened and only until the loss of pressure is observed at the gauged or through the sound of air loss (if the pump gauge is decent you’ll probably see it before you hear it). Stop (don’t undo the pump any further than the first sign of pressure change) and let the air slowly leak out. At this point we have one of two conditions at play- either there are (1) two separate air chambers (the Schrader valve has previously closed sealing the suspension from pump) OR (2) the suspension air chamber and the air chamber of the hose/pump are still connected and the valve is open. By now the hiss has subsided and the pump reads 0 PSI. Now, if condition (2) was in play the pump would have leaked and since the valve was open pressure would decrease in both, eventually reaching zero PSI in both*. However, if the Schrader valve had closed before the air pressure began to decrease there is still going to be FULL pressure in the shock. That’s it. If the valve is open the air will leak from the shock into the pump as soon as the shock loses seal. If not, the valve closed before any pressure differential could occur. It can be only one or the other.
Does that make sense or am I explaining it terribly? I tend to do that.
*one minor thing to consider- the valve spring on the Schrader would probably close the valve before the PSI reached zero but it would likely be less than 1 PSI. THAT would actually be a fun thing to determine LOL
Oh I totally follow, I had somewhat misread your previous post. I agree that in theory should answer the question. I need to work on the bike tonight, I may just pour myself a bourbon and find out.
Set suspension to X pressure Remove pump. Screw pump back on until you can build pressure in the pump but the valve on the shock hasn’t been opened yet.
Pump the pressure in the shock pump to X
This should put the pressure in the pump gauge and hose to the same as your shock before the shock valve opens.
Second, you can lose pressure when disconnecting the pump – at least with my pump. If I disconnect it quickly, it’s not significant. If I disconnect it slowly, it clearly loses pressure.
Are you certain about that? It’s a common misconception but if you truly are you’ve either got a defective or poorly designed pump or your valve is damaged.
Okay, seems I was wrong. No issue when removing my pump slowly. Must be when I remove my ShockWiz that I’ve had that issue. The hoses for it probably aren’t designed to allow the valve to close before breaking the connection.
I now agree that there should be no pressure loss when disconnecting a pump if properly designed.
but for those pump that does not have the red knob. I believe it designed in such a way that when you start unscrewing the pump valve, it will close up the schrader valve while it is still pressurized. And the hissing sound of air is the one that coming from the the pump. If it isnt designed that way. Im glad i got the bontrager one:blush:
. I want to get the digital Fox one but it’s out of stock.